# std::ranges::views::join_with, std::ranges::join_with_view

From cppreference.com
< cpp‎ | ranges

Defined in header `<ranges>` |  |
template< ranges::input_range V, ranges::forward_range Pattern > requires ranges::view<V> && ranges::input_range<ranges::range_reference_t<V>> && ranges::view<Pattern> && /*concatable*/<ranges::range_reference_t<V>, Pattern> class join_with_view : ranges::view_interface<join_with_view<V, Pattern>> | (1) | (since C++23)
namespace views { inline constexpr /* unspecified */ join_with = /* unspecified */; } | (2) | (since C++23)
Call signature |  |
template< ranges::viewable_range R, class Pattern > requires /* see below */ constexpr ranges::view auto join_with( R&& r, Pattern&& pattern ); |  | (since C++23)
template< class Pattern > constexpr /* range adaptor closure */ join_with( Pattern&& pattern ); |  | (since C++23)

1) A range adaptor that represents `view` consisting of the sequence obtained from flattening a view of ranges, with every element of the delimiter inserted in between elements of the view. The delimiter can be a single element or a view of elements.
For the definition of /*concatable*/, see `std::ranges::concat_view`.
2) RangeAdaptorObject. The expression views::join_with(e, f) is expression-equivalent to join_with_view(e, f) for any suitable subexpressions e and f.

`join_with_view` models `input_range`.

`join_with_view` models `forward_range` when:

- ranges::range_reference_t<V> is a reference, and
- `V` and ranges::range_reference_t<V> each model `forward_range`.

`join_with_view` models `bidirectional_range` when:

- ranges::range_reference_t<V> is a reference,
- `V`, ranges::range_reference_t<V>, and `Pattern` each models `bidirectional_range`, and
- ranges::range_reference_t<V> and `Pattern` each model `common_range`.

`join_with_view` models `common_range` when:

- ranges::range_reference_t<V> is a reference, and
- `V` and ranges::range_reference_t<V> each model `forward_range` and `common_range`.

### Nested types

Type | Definition
`InnerRng` | ranges::range_reference_t<V> (exposition-only member type*)

### Data members

Member | Definition
`V` `base_` | the underlying (adapted) view (exposition-only member object*)
`Pattern` `pattern_` | the pattern object (exposition-only member object*)
`non-propagating-cache`﻿<ranges::iterator_t<V>> `outer_it_` (present only if `V` does not model `forward_range`) | the cache of the outer iterator (exposition-only member object*)
`non-propagating-cache`﻿<std::remove_cv_t<`InnerRng`﻿>> `inner_` (present only if std::is_reference_v<`InnerRng`﻿> is false) | the cache of the inner range (exposition-only member object*)

### Member functions

(constructor) | constructs a `join_with_view` (public member function)
base | returns a copy of the underlying (adapted) view (public member function)
begin | returns an iterator to the beginning (public member function)
end | returns an iterator or a sentinel to the end (public member function)
##### Inherited from std::ranges::view_interface
empty | returns whether the derived view is empty. Provided if it satisfies `sized_range` or `forward_range`. (public member function of `std::ranges::view_interface<D>`)
cbegin (C++23) | returns a constant iterator to the beginning of the range. (public member function of `std::ranges::view_interface<D>`)
cend (C++23) | returns a sentinel for the constant iterator of the range. (public member function of `std::ranges::view_interface<D>`)
operator bool | returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of `std::ranges::view_interface<D>`)
front | returns the first element in the derived view. Provided if it satisfies `forward_range`. (public member function of `std::ranges::view_interface<D>`)
back | returns the last element in the derived view. Provided if it satisfies `bidirectional_range` and `common_range`. (public member function of `std::ranges::view_interface<D>`)

### Deduction guides

### Nested classes

iterator | the iterator type (exposition-only member class template*)
sentinel | the sentinel type (exposition-only member class template*)

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_ranges_join_with` | `202202L` | (C++23) | `std::ranges::join_with_view`

### Example

Run this code

    #include <iostream>
    #include <ranges>
    #include <string_view>
    #include <vector>

    int main()
    {
        using namespace std::literals;

        std::vector v{"This"sv, "is"sv, "a"sv, "test."sv};
        auto joined = v | std::views::join_with(' ');

        for (auto c : joined)
            std::cout << c;
        std::cout << '\n';
    }

Output:

    This is a test.

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 4074 | C++23 | `join_with_view` was underconstrained | updated the constraints

### See also

ranges::join_viewviews::join (C++20) | a `view` consisting of the sequence obtained from flattening a `view` of `range`s (class template) (range adaptor object)
ranges::concat_viewviews::concat (C++26) | a `view` consisting of concatenation of the adapted views (class template) (customization point object)

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